Electrical insulation



Patented Dec. 5, 1933 UNiTE STATES PATENTE FFICFE ELECTRICAL INSULATION Application March 10, 1930. Serial No. 434,832

' 6 Claims. (01. 173-264) My invention relates to improvements in the compounding of rubber for electrical insulation; my invention includes new rubber insulating products and a method of improving electrical properties of rubber insulating compounds.

Hitherto, the presence of carbon black in rubber insulating compounds has been regarded as detrimental because of its conducting properties, and, so far as I am aware, carbon black has never intentionally been added as such to rubber insulating compounds. Reclaimed rubbers containing carbon black derived from the reclaimed coir'ipound'or added during the reclaiming operation have, to some extent, been included in immler-insulating compounds; but in such instances the carbon black has not been added as such to the insulating compounds, only as an incidental component, of the reclaimed rubber.

{have discovered, contrary to the accepted fpfactice' of excluding carbon black; as such from. insulating compounds, that certain electrical.

properties 'of rubber insulating compounds are improved by an appropriately addition'of carbon black as such. In the practice of my in-- ggiventiomto secure the advantages of-my inven tion, the carbon black must be added the rubber, insulating compound as such, that is, the carbon black mustliave-when incorporated in the insulating lcompound the adsorptive capacity of raw giuncomnounded carbon black, Als0, the carbon black 'is best substantially free from moisture. i

To illustrate: l .have discovered that the. ele ctrical breakdown strength of some,,rubber insuei igsaei u d sen e 't sed ,fo e. as F s e l t-+6. 0 or mor r be addition.

forfexaznpleoi 2-4,% by Weight, on a compound; containing ifo example, 20-40% of rubbe of carbonblack as such. in referring. to fbreakdown, strength, I refer tothe minimum-value of.ap.- plied electrical potential per. unit 'of thicknessunderlwbich th'e' insulating compound will rup-' "1 j, ing6% byweighton the compound-.

n to. illustrate I have; discovered that some ru ber insulating compounds can be im ture '5 gproved withrespect to power factor. bythe additid pjq' d'cont'aining, for example, 20-40 of rubber.- ofcarbon black as such. In referring to power. factorfi lrefer'to the tendency of the insulating compound "to dissipate electrical. energy when subjected to alt'ernating potentiaL' sunfurther to illustrate: 1 have discovered,

e f' h ef i iwor some rubber insulating o pounds'can' be increased, for example, by as black-as such. In referring" to "resistivity", I refer to'the'specific resistance per unit of thick ne'ssof the insulating compound.

'fonxamplegof ii-4%.by weight, on a. com-,

much as50 or more-by'the addition, for'ex-' ample, of 254% by weight, on a compound containing, for example, 20-40% of rubber, of carbon 7 So far as I can determine, this unexpected result seems to be due to the adsorptive capacity of the carbon black. With the utmost care, the absolute exclusion of water and even electrolytic constituents probably isnever accomplished, with the result that water and-electrolytes, perhaps in butthe most minute amounts, are always present. Apparently the adsorption of such electrolytes renders them less active as a deteriorating influence with respect to electrical properties of the insulating compound while-the advantage so secured by the adsorption of such electrolytes on added carbon blackoverbalancs, within limits, any disadvantage incident to the addition of the carbon black. The renderingof such adsorbed electrolytes less active mayin part be due to the conducting properties of the carbon black. However, I do not predicate my invention upon this oranyotherhypothesis.

Whatever the explanation, I have found that electrical properties of rubber insulating compounds are improved by an appropriately limited addition of carbon black. The exact proportion of carbon black to be used for best results varies with difierent compounds and, probably, .2 with compounds of diflerent purity. Also, the several electrical properties of the insulating-compound are notuniformly afiected, so that .the. proportion depends "in some cases upon the propertyto be brought to optimum value. I The proportion apparently approidmates that'j'ust 'sufllcient to absorb electrolytes present in the insulating compound. Best results are usually secured" with an amount of carbon black approximating up to 10% by weight on -.the ,rubber conten t- ,oi the compound (crude rubber plus the content of any reclaimed rubber in the compound);- and usually not substantially exceeding 3% by weight on the compound, although optimum ,values are sometimes secured with an amount .of carbon black exceeding 3% but not substantially exceedthe amount of carbon black incorporated in the insulating'compound' 'is increased, the "effect 'of its conducting properties becomes apparent in rendering the compound of diminishing value as electrical insulatiom in conformity with the principle of accepted practice, but with appropriately additions, in; accordance with my invention, this effect, if is. exists, disappears in the improvements efiectedby; the addition. My invention is directed to range of additions within whichthe electrical property or properties are improved-by the addition of carbon black as compared to such property'orproperties of the compound without the carbon black.

It is conceivable that a rubber compound might be so poor, electrically, without the addition of carbon black, that'irnprovement, with respect to certain electrical properties, such as electrical breakdown strength or power factor, for example, might still be noted with additions of carbon black so large as to make the compound 5 useless as electrical insulation because of the 9846 rubber (smoked sheets) 30.0 zinc oxide 29.0 carbon black 3.5 tetra metlwl-thiuram-monosulfide 40.0 sulfur This insulating compound includes about 2.9% by weight on the rubber and about 2.7% by weight on the compound of carbon black added assuch; this insulating compound is a particularly advantageous embodiment of my invention;

974.3 rubber (smoked sheets 30.0 zinc oxide 48.3 carbon black A 3.5 tetra methyl-thiuram-monosulfide 40.0 sulfur This insulating compound includes about 5.0% V by weight on the rubber and about 4.4% by weight on the compound of carbon as such.

409.0 rubber (smoked sheets)- 250.0 champion reclaim (acid-reclaimed rubber) a 90.0 zinc oxide 200.0 mineral rubber 5.8 anti-oxidant (agerite) 20.0 carbon black 1.0 tetra methyl-thiuram-monosulfide 22.0 sulfur lhis insulating compound includes about 3.9,.%.

by weight on the rubber and about. 2.0% by weight on the compound of carbon, blackadded as this insulating compoundis aparticularly adv an; tageous embodiment of invention.

409.0 rubber (smoker-sheets) 250.0 champion reclaim (acid-reclaimed rubber) 30.0 zinc oxide 200.0 mineral rubber 5.8 anti-oxidant 40.0 carbon black I 1.0 tetra methylthiuram-monosu1fide 22.0 sulfur This insulating compound. includes about 7.9 by weight on the rubber and about 4.2% by weight on the compound of carbon black added as such.

4000 rubber (smoked sheets) 250.0 Philadelphia. #200jreclaim reclaimed rubber) 218.0 zinc oxide 5.8 anti-oxidant 15.5 carbon black 10.0 master batch-accelerator 22.0 sulfur lk icompound as well eijfecting'; improvement electrical properties. A substantialeco'nomy may 172.5 zinc oxide 200.0 mineral rubber 5.8 anti-oxidant 31.0 carbon black 10.0 master batch-accelerator 22.0 sulfur This insulating compound includes about 5.6% by weight on the rubber and about 2.8% by weight on the compound of carbon black added as such'; this insulating compound is a particularly advantageous embodiment of my invention.

9-0. Rubb m sheets) 2. .0.0 P i a p a 00 re k re im r be 126.0 zinc oxide 200.0 mineral rubber .-8. ent r x d 'nt. 4. 1 car on. black. .0-0 .nias e ba h-acce rator This insulating compoundincludes about 8.5%

by weight'on the'rfubber and about 4.4% by weight on the compound ot carbon black added assuch.

The foregoing insulating compounds are inparts by weight.- Themes er batch-accelerator component 'of'each of the lastcompounds" consists of a mixture of'90%- of rubber and 10% of tetra methyl-tbiura'm-monosuliide by weight. The anti-oxidant component of each f'the la'st five compounds ls'a condensationproduct o acetaldehyde and alphanaphth'ylaxnine'. Each of the foregoing insulating compounds maybeapplied to wire, for-example, and ;-vulcani2e'd thereon in the conventionalinannri' The 'vul canization may correspondffor example .to 5.1 platen press fcure= '01 "twenty-five fat. F5 I j A 4- invention is of special value and; appliea; tion in connection withjinsulatingjompounds: including alkali-reclaimed rubberr'the invention seems to be' peculiarly etlecti ve i efiectipg' improvement ofsuchinsulatinglcompqunds sj The invention also has anothe" a insulating compounds mcmgnigzniatxmgg hi such compounds, tli'a rbon pia kaudeii; suc i r. to the coir'ipound; inaccordance with'myjin'yen -f tion may-besubstitutedior ei nal iabs'olute volume of -'z' ind oxide the compound-, th e carbonblack thus replacing zinc oxide in the insulatin expensive" than zinc oxide as f'a "co' meteriah. r

The invention has important-advantage Q11 th e tin am; instanc s 9 p op r i of an in ul n pi glun a.

thus be effected since carbon black mgch le ss qn i. mnot anc w th a. rial'fi b fis arbon black. th anee-. .p 9n0ztibnsused in accordance with ipypdtiomnrate, ally. im r ves. the t nsi e.- n h. toflghnesi resilience, tear resistance and resistance mabra sion. o r bb nsu ating omp unds. n h s aspectthe invention. proxides for joint improve-# ment of, physical andelectrical. prope ties of; 111- l'a e Compound mpa cu ar. s ae t the invention provides. for. i1nprogvement.otphysicaL'properties of. rubber insulating-compounds applied directly ta wire, or other.conductor 59 where such improvement is normally diflicult or impossible of attainment because the electrical properties are particularly important.

The invention is furtherillustrated by reference to the annexed drawing which represents conventionally two types of insulated electrical conductors contemplated by my present invention. It is, to be understood, however, that this further illustration is for exemplification only and my invention is not limited thereby.

Fig. 1 of the drawing represents one aspect of my invention in accordance with which a layer of my improved rubber insulation 2 is applied directly to the electrical conductor 1.

Fig. 2 represents a modification of my invention in accordance with which the electrical conductor 1 is not in direct contact with myimproved rubber insulating material 2 but is separated therefrom by a layer of non-rubber insulation material 3, for instance cotton or the like.

In referring to carbon black," I intend to distinguish from lamp black. It is with appropriately limited additions of carbon black as such that the advantages of the invention are secured. Of the commercial carbon blacks, "Micronex", for example, is suitable for the practice of my invention and Micronex may be used with advantage in the foregoing illustrative insulating compounds. ,I

As previously mentioned, in the practice of my invention and to secure the advantages of my invention, the carbon black must be added to the rubber insulating compound in its raw state, i. e., the carbon black must have, when incorporated in the insulating compound, the adsorptive capacity of raw uncompounded carbon black. To illustrate; Philadelphia #200 reclaim, mentioned as a component of the last three of the foregoing illustrative insulating compounds, includes about 7.5% by weight of carbon black. This carbon black, however, is not effective for the purpose of my invention, apparently because its adsorptive capacity has been exhausted in the reclaimed compound. Carbon black so added to the insulating compound as an incidental compound of reclaimed rubber is not raw carbon black, or carbon black added as such in accordance with my invention. It is to make this distinction that I refer, in the claims, to raw carbon black.

The process of my invention comprises" the addition of carbon black as such to rubber insulating compounds in amount just suflicient to improve or to bring to optimum value the important electrical property or properties; for example, suflicient to reduce the power factor of the compound to a minimum or to make it less than that of the compound without the carbon black, or suflicient to increase the breakdown strength of the compound to a maximum or to make it greater than that of the compound without the carbon black, or suflicient to increase the resistivity' of the compound to a maximum or to make it greater than that of the compound without the carbon black. The process 'of my invention also comprises the addition of carbon black as such to rubber insulating compounds in amount appropriate to secure, jointly with such improvement of the important electrical property or properties, improvement of physical properties of the insulating compound.

I claim:

1. An electrical conductor having a rubber insulation thereon, the rubber nearest the conductor containing dry raw carbon black in amount not substantially less than 1.4% and not substantially exceeding 3% by weight on the compound.

2. An electrical conductor having a rubber insulation thereon, the rubber nearest the conductor containing dry raw carbon black in amount not substantially less than 1.4% and not substantially exceeding 6% by weight on the compound.

3. An electrical conductor having a rubber insulation thereon, the rubber nearest the conductor containing dry raw carbon black in amount not substantially less than 1.4% and not substantially exceeding 10% by weight on the compound.

4. An electrical conductor insulated primarily by rubber, the major portion of said rubber insulation containing dry raw carbon black in an amount not substantially less than 1.4% and not substantially exceeding 3% by weight on the compound.

5. An electrical conductor insulated primarily by rubber, the major portion 01' said r her insulation containing dry raw carbon blac in an amount not substantially less than 1.4% and not substantially exceeding 6% by weight on the compound.

6. An electrical conductor insulated primarily by rubber, the major portion of said rubber insulation containing dry raw carbon black in an amount not substantially less than 1.4% and not substantially exceeding 10% by weight on the compound.

WILLIAM BRYANT WIEGAND. 

